In the operation of injection molding process, it is common to preheat the female die and male die to a specific temperature before the two dies are integrated for injection since the preheated mold can prevent the melted plastic from cooling down too rapidly and becoming somewhat “sticky” and thus ensure the melted plastic that is being injected into the same through its sprue gate, to flow smoothly therein and arrive at the mold cavity for molding.
It is noted that the conventional preheating structures for injection molds, which can be electric heaters or high-frequency heater, are fixed heaters being fitted inside either the female die or the male die of the injection molds. As a conventional high-frequency mold structure shown in FIG. 1, the male die 11 and female die 12 are configured with inserts 13, 14 in respective while there is an electric heating coil 16 and cooling pipe 17 being configured inside the male die 11 and a sprue gate 15 for the mold structure being formed on the female die 12. The electric heating coil 16 is activated for preheating the male die 11 before the two dies 11, 12 are integrated and clamped, and then the two dies 11, 12 can be integrated and provided for a melted plastic to be filled therein through the sprue gate 15, by that since the preheating can prevent the melted plastic from cooling down too rapidly, the melted plastic is able to solidified and molded correctly inside the mold structure, and thereafter being cooled down by the cooling pipe 17 for preparing the final product of the injection molding to be detached from the mold structure.
Nevertheless, the aforesaid conventional mold structure is shorted in the sizes of its male die and female die as they can be very big and bulky. As a larger die will required a longer time for preheating the same to a specific temperature, the production time for an injection molding process using the mold to produce a product is prolonged and consequently the production yield of the injection molding is adversely affected. Not to mention that the lager a die is, the more energy it will need for the preheating which not only is not energy efficient, but also can be very costly. Moreover, as there is cooling water kept circulating inside the cooling pipe even at the time when the electric heating coil is activated for preheating the male die or female die, the male die or female die is being cooling down as it is being heated which not only might prevent the same from being heated to the specific temperature, but also can waste a lot of energy.
Except for the aforesaid internal heater embedded inside the die, there are external preheating structures for preheating the mold, as the heater 20 shown in FIG. 2. The heater of FIG. 2 is composed of a burner 21 and a fuel pipe 22, in which as the fuel pipe 22 is connected to the burner 21 by an end thereof while another end of the fuel pipe 22 is connected to a fuel supply, fuel can be fed to the burner 21. As shown in FIG. 2, the flame 23 from the burner 21 of the external heater 20 is adapted for heating a forging mold for forging machines or an injection mold for injection molding as the molds are composed of a top die 24 and a bottom die 25 and thus the temperatures of the heated molds can be increased from room temperature to a working temperature. Nevertheless, although the aforesaid external heater is able to achieve the expected preheating effect, it can be very time-consuming and difficult to apply that it is only suitable for large-size forging machines or injection molds, and is not adapted for molds of precision injection molding.
In addition, there is a conventional preheating structure that is configured with a hollow heating coil whereas the hollow heating coil is structured for allowing cooling water to flow inside the hollow coil. However, as the cooling water is flowing inside the heating coil, the cooling water is not able to cool down the corresponding mold effectively and thus the heat dissipating efficiency of the mold is poor. If a better cooling effect is required, it is required to increase the inner diameter of the heating coil for increasing the flow of the cooling water, but at the cost of larger and heavier heating coil.
There are already many heating devices for mold preheating, as those disclosed in TW Pat. Appl. No. 92123778, TW Pat. Appl. No. 92123775 and TW Pat. Appl. No. 94127663. In the driving device for instant mold preheating module disclosed in TW Pat. Appl. No. 92123778, the inserts in a mold will first be identified and driven by the driving device for enabling the same to be preheated during the clamping process for die integration, As the volumes of the inserts are usually comparatively smaller, they can be heated to a specific temperature rather fast. Moreover, also as the inserts are small in size, they can be cooled down equally fast after the melted plastic had filled uniformly in the mold cavity and after mold injection. As the instant mold preheating module in the aforesaid TW patent is a high-frequency induction heating device packed inside ceramics or plastic steel, which can be fitted inside grooves formed on the inserts for using the eddy currents from the heating device to heat up the inserts to a specific temperature in an instant manner. Thereby, not only the time required for preheating the mold is decreased, but also the preheating efficiency of the mold is improved. On the other hand, the instant heating method and device of molding equipment disclosed in TW Pat. Appl. No. 92123775 is an improvement over that disclosed in TW Pat. Appl. No. 92123778. In TW Pat. Appl. No. 92123775, the high-frequency induction heating energy is designed to work directly on the inserts of a mold for heating the surfaces of the same to a specific temperature in an instant manner, by that not only the preheating efficiency is improved with less energy consumption, but also it can ensure the melted plastic to flow smoothly in the mold cavity for molding. Furthermore, the device disclosed in TW Pat. Appl. No. 94127663 is further an improvement over the one disclosed in TW Pat. Appl. No. 92123775. In the TW Pat. Appl. No. 94127663, the connection between the heating coil and the transformer is redesigned and structured for enabling the two to be detachable, so that the preheating device can be move easily and rapidly around a mold so as to be used for preheating any portion of the mold in a precise manner.
However, those prior-art preheating devices are only aimed for the improvement in preheating efficiency. Thus, it is in need of a preheating device capable of fitted to a mold to be used for enhancing the preheating efficiency of the mold while reducing the time required for cooling the mold.